Ureteral stents are used to assist urinary drainage from the kidney to the urinary bladder in patients with a ureteral obstruction or injury, or to protect the integrity of the ureter in a variety of surgical manipulations. Stents may be used to treat or avoid ureteral obstructions (such as ureteral stones or ureteral tumors) which disrupt the flow of urine from the kidneys to the bladder. Serious obstructions may cause urine to back up into the kidneys, threatening renal function. Ureteral stents may also be used after endoscopic inspection of the ureter to prevent obstruction of the ureter by swelling of the ureteral wall caused by the surgical procedure.
Ureteral stents typically are tubular in shape, terminating in two opposing ends: a kidney distal end and a bladder proximal end. One or both of the ends may be coiled in a pigtail or J-shape to prevent the upward and/or downward migration of the stent due, for example, to physiological movements. A kidney end coil resides within the lumen of the kidney, known as the renal pelvis, and is designed to prevent stent migration down the ureter and into the bladder. The bladder-end coil resides in the bladder and is designed to prevent stent migration upward toward the kidney. The bladder coil is also used to aid in retrieval and removal of the stent. Regions such as the trigone region in the bladder and the region of the ureter near the bladder known as the ureteral-vesical junction are particularly innervated and thus sensitive to irritation by foreign objects. Commonly used bladder-end coils contact and irritate the trigone region causing discomfort to the patient. Similarly, the proximal region of the stent contacts the ureteral-vesical junction causing irritation and discomfort to the patient particularly during voiding. Additionally, ureteral stents, particularly the portion positioned within the ureteral-vesical junction and inside the bladder, may produce adverse effects including blood in the urine, a continual urge to urinate, strangury, and flank pain accompanying reflux of urine up the stent (e.g., when voiding). Such effects occur as pressure within the bladder is transmitted to the kidney. In short, while providing drainage from the kidney to the bladder, stents may also cause or contribute to significant patient discomfort and serious medical problems.